P13E-01
Laboratory Studies of the Heterogeneous Uptake of Methane on Martian Soil Analogs: Determination of Upper Limits of Reactivity
In order to constrain possible methane sources on Mars, it is necessary to understand the type and magnitude of all possible methane sinks. We have performed laboratory experiments to determine the importance of heterogeneous uptake of methane on mineral surfaces analogous to Martian surface material. The uptake of methane on sodium montmorillonite and Mars soil simulant JSC-1 (a palagonite) was studied using a Knusden cell flow reactor capable of achieving Martian temperature, pressure and relative humidity conditions. A quadrupole mass spectrometer was used to detect any decrease in methane flow due to heterogeneous uptake and infrared spectroscopy was used to detect any adsorbed species on the particles. Experiments were performed under Martian temperatures (from 195 to 215 K), and under both dry conditions and 45% RH. As montmorillonite clay possesses unique swelling properties in the presence of water vapor, experiments were performed in which the clay was simultaneously exposed to water and methane, and also experiments in which the clay was equilibrated with water vapor prior to methane exposure. We found no methane uptake relative to an unreactive blank Si wafer on any of the Martian soil analogs studied under any conditions. These negative results place upper limits on the heterogeneous reactivity of methane on the Martian surface. We have determined that the initial uptake coefficient of methane on palagonite is less than 3.66×10-10 (±1.41×10-11) and the initial uptake coefficient, γ0, of methane on montmorillonite is less than 7.52×10-10 (±2.56×10-11). These studies demonstrate methane uptake by mineral surfaces is not expected to be a significant methane sink, as the process likely occurs on a time scale much longer than photolysis.
P13E-02 [WITHDRAWN]
Chemical Implications of Electric Discharge for Methane in the Martian Atmosphere - Laboratory Simulations
Methane is still one of the most debated species in the martian atmosphere. The search for methane in the martian atmosphere has led to variable concentration estimates, from none to 10 ppbv globally. Different theories have been proposed to explain this variability. One proposed destruction mechanism for methane is breakdown through electric discharge induced chemistry. This discharge could be induced on Mars by electric fields generated by dust particle interaction in dust storms and dust devils. Theoretical models describe the processes that could occur in the martian atmosphere and provide estimates of breakdown voltages and chemical reaction schemes of breakdown products. In order to test these predicted breakdown scenarios, we have built a laboratory setup to simulate these processes. With this setup we will not only measure the breakdown rates and products of methane in the martian atmosphere, but it also enables to measure formation products such as hydrogen peroxide. Hydrogen peroxide has been suggested to play a role in the desctruction of organics on the martian surface. We will present the first results from our experiments as well as the implications for the methane cycle on Mars.
P13E-03 INVITED
Interpreting a Weathered Mars: Investigating the Effects of Weathering on Spectroscopic Observations Through Laboratory Study
Infrared spectroscopy is a critical tool for Martian mineralogy. Because it is crucial to evaluate the history of water on Mars, mineralogical study of weathering and alteration is among the most important topics of Mars spectroscopy. The state of alteration of the Martian surface is evaluated by the presence or absence of alteration phases and their overall abundance. Interpretations of Martian weathering processes are based on the types of alteration products, the mineral assemblages, and derived chemistry. The spectroscopy of alteration minerals has been studied in detail for decades; however, detecting and identifying alteration products from remotely- sensed spectra of natural surfaces is complicated by microtextural mixing of rock-forming minerals, alteration products, and void space. We are investigating the effects that low-temperature weathering has on spectral observations in order to facilitate interpretation of spectroscopic data of Martian surfaces that may be weathered. Our approach has been to characterize the infrared spectra, mineral assemblages, and textures of weathering rinds and rock coatings formed on volcanic rocks in a variety of environments. This approach enables us to witness the spectral variability that results from weathering and tie it to differences in texture or mineralogical composition. More importantly, by examining numerous rinds and coatings, we can determine what effects are common to broader weathering phenomena. For instance, basalt weathering typically leads to systematic changes in silicate vibrational absorptions that can hamper spectral modeling techniques used to assess Martian data. In addition, weathered surfaces may show little evidence of hydrated minerals in near-infrared data. Another important component of our research is the use of controlled laboratory experiments designed to simplify, yet emulate, important attributes of the naturally weathered surfaces, in order to better constrain the spectral effects of weathering. Based on our findings regarding weathering mineral detectability, assertions that Mars has lacked aqueous weathering in its latter history may be incorrect. Rather, we suggest that volumetrically small amounts of high-silica weathering products formed in aqueous environments at middle and high latitudes and that this is consistent with spectroscopic observations of Mars.
P13E-04
Thermal Infrared Studies of Chloride Salts; Implications for Mars
Morphological and spectral evidence supporting the past occurrence of widespread water on the surface of Mars continues to build. Furthermore, geochemical footprints of water are especially compelling. As a past reservoir of water receded, it would have left behind evaporitic chemistries specific to Martian water-rock interactions (e.g. chlorides, sulfates and phyllosilicates). To understand the extent and abundance of past water, the detection of such minerals is key. In support of both orbital and in situ thermal infrared (TIR) observations, we have examined the TIR behavior of chloride minerals. In the thermal infrared, most minerals are identified based on characteristic absorption features. However, chloride detection is particularly challenging because these minerals are transparent over much of the infrared and therefore their identification must be based on the effect that they have on the spectra of coexisting materials. Additionally, the transparent nature of chlorides results in greybody (non-unit emissivity) behavior and consequently the standard calibration techniques to convert from radiance to emissivity produces a slope in the spectra. Here we discuss laboratory spectral studies including emission, reflectance, and transmission spectra of a suite of chloride minerals and mixtures. These studies are then used to interpret a spectrally distinct deposit identified with 2001 Odyssey Thermal Emission Imaging System (THEMIS) data in the low albedo, mid-to-low latitude, southern highlands of Mars which correspond to mid- late Noachian aged terrains and early Hesperian aged ridged plains units.
P13E-05
Thermal Infrared Spectroscopy of Experimentally Shocked Plagioclase and Basalt and Applications to Mars
Laboratory thermal infrared emission spectra (250-1400 cm-1) of experimentally shocked (17-60 GPa) plagioclase feldspars (bytownite, andesine, and albite), basalt, and basaltic andesite demonstrate the disordering of mineral lattices and increasing glass content with increasing shock pressure. These effects cause loss of spectral detail and shifts in absorption feature positions. Disordering in the feldspar structure begins at pressures >15-20 GPa, and diaplectic glass (maskelynite) formation is complete between ~30-45 GPa. As pressures increase the mutual existence of crystalline phases and diaplectic glasses cause the characteristic, fourfold (tetrahedral), strong coordination bonds of Si and Al in feldspars to alter to weaker, less polymerized bonds that approach sixfold (octahedral) coordination. This influences the characteristic vibrational frequencies in the thermal infrared. For example, the bands near 400-550 cm-1 are caused by bending vibrations in the Si-O-Al planar ring structures in tectosilicates and diaplectic glasses. Si-O-Si octahedral bending vibrations cause absorptions between about 700-450 cm-1 and SiO6 octahedral stretching vibrations occur between 750-850 cm-1. Absorptions in the 900-1200 cm-1 region are due to Si-O antisymmetric stretch motions of silica tetrahedra. Many of these spectral features persist to higher pressures in albite compared to bytownite, possibly due to the relatively lower Al content in albite. With increasing Ca content, the main absorption band of highly shocked albite shifts from ~1050 cm-1 to ~1000 cm-1 for andesine and ~950 cm-1 for bytownite. However, the other main absorption in highly shocked feldspars near 450-460 cm-1 varies little with Ca content. Linear mixing models demonstrate that mineral and glass spectra cannot replicate shocked bytownite spectra beyond shock pressures of 20-25 GPa, coincident with the onset of diaplectic glass formation. Similar models of shocked basalt also exhibit increased errors beyond 20-25 GPa unless spectra of shocked feldspar are used in spectral libraries. Ongoing spectral mixing analyses of Thermal Emission Spectrometer (TES) data using spectra of shocked feldspars suggest that semi- contiguous regions of shocked materials worthy of further study are found in Solis Planum, Acidalia, Syrtis Major, and northern Utopia.
P13E-06
Linking Surface and Cumulus Lithologies on Mars: Evidence From Experimental Phase Relations
A major crustal differentiation process in regions of thick crust on Earth is deep-seated fractionation. In this process, the crystalline material formed at depth through crystallization of mantle-derived magma ponded at or near the base of the crust remains in the lower crust while residual liquids ascend to the upper crust. An example of this process on Mars is afforded by the volcanic rock Backstay analyzed by the MER Spirit and the Chassigny dunite of the SNC meteorites. Experimental investigation of phase equilibria of Backstay composition liquids indicates that at the base of the Martian crust Backstay composition liquid with 1 wt% water is saturated in the cumulus minerals of the meteorite and, upon further crystallization, produces the mineral assemblages of the polyphase melt inclusions. The residual liquids become increasingly silica-rich, alumina-rich and Na-rich, and the Fe contents become increasingly similar to those of alkalic suites on Earth. Depending upon the temperature of separation of the residual liquid from the accumulating minerals, the residual material varies from dunitic to gabbroic. The compositional characteristics of the evolved alkalic liquids are not reflected in bulk surface chemistry of the planet which suggests that as on Earth alkalic rocks may be rare on Mars. Such experimental investigations are being applied to other Martian surface lithologies (i.e., Humphrey, Irvine) in order to identify further links between the cumulus meteorite lithologies and surface igneous lithologies, and in order to constrain possible igneous processes responsible for inducing compositional variability of the martian crust.
P13E-07
Experimental Crystallization of Dry and Wet Humphrey at 9.3 kbar: Implications for Compositional Diversity of the Martian Crust
In regions of thick crust on Earth, igneous compositional diversity arises readily by fractionation of mantle-derived magmas at depth and ascent of residual liquids into the upper crust at various stages of fractionation. This process appears to have also occurred on Mars as evidenced by the relationship between the composition of the surface rock Backstay (analyzed by the MER Rover Spirit in the Columbia Hills of Gusev Crater) and the mineralogy of the Chassigny dunite (Nekvasil et al., this conference). In addition to the likely diversity caused by such a process, additional compositional diversity can arise from differing amounts of bulk water in the parental magma. The goal of this work is to understand the effect of water on derivative melt compositions when crystallization occurs at the base of the martian crust. The liquid composition chosen was that of Humphrey of the Adirondack class basalts analyzed by the MER rover Spirit in Gusev Crater, Mars. The Adirondack class basalts are picro-basalts with some evidence of olivine accumulation, however, they are considered by many to represent primitive basalt compositions. The Humphrey composition was created by mixing powdered oxides, Fe sponge, CaF2, and NaCl. Experiments on the powdered mix were conducted in piston-cylinder presses at 9.3 kbar using graphite capsules and BaCO3 cells. Nominally dry experiments were conducted by drying the powder in a pot furnace at 800°C for 20 minutes to drive off structural and absorbed H2O before being loaded into the piston- cylinder press. Wet experiments were conducted at 1 wt% H2O, and were created by synthesizing a hydrous glass of Humphrey composition with ~4 wt% H2O and mixing this hydrous glass with dry Humphrey mix proportionally such that 1 wt% bulk H2O would be achieved. All water contents were verified by micro- FTIR, and all run products were analyzed by electron microprobe. The liquid line-of-descent for nominally dry experiments follows a silica-depletion trend as is observed for similar terrestrial compositions. Residual liquids are enriched in Fe, Ti, and P, which is also observed terrestrially in fine- grained FTP rocks of anorthosite complexes (e.g., the Laramie anorthosite complex) and in lavas of the Snake River Plain. The liquid line-of-descent for experiments with a starting bulk H2O content of 1 wt% follows a silica-enrichment trend consistent with being on a path towards more rhyolitic compositions. Residual liquids are enriched in Si, Al, Fe, and alkalis. This is in keeping with experiments on a terrestrial tholeiite with starting bulk water contents greater than 0.4 wt%. Ascent of these residual liquids into the upper crust would result in very different bulk compositions depending upon bulk water content. If the compositions of martian soils and bulk surface reflect primarily an igneous substrate without major sedimentary re-working, then the compositions suggest that magmas added to the martian upper crust were likely low in bulk water content.
P13E-08
Magnetic Characterization of Synthetic Martian Basalts and Implications for the Surface Magnetization of Mars
A suite of synthetic Martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data. We systematically evaluate the effects of major element composition, oxygen fugacity (fO2), and cooling rate on phase chemistry and magnetic mineralogy, grain size, and intensity of remanent magnetization. The range of experimental compositions and fO2 are chosen to bracket the range expected in the Martian crust; our results should therefore bracket the range of possible mineralogies, textures, and magnetic properties in rapidly-cooled Mars crustal materials. Two basic starting compositions are used for the sample synthesis. The first is Fe-rich, Al-poor and is patterned after SNC basaltic meteorites. The second has a much lower Fe/Al ratio and is based on satellite thermal emission spectrometer observations of the southern highlands that suggest a more terrestrial-like composition. fO2 varies between the iron-wustite (IW) and quartz-fayalite-magnetite (QFM) buffers. The resulting magnetic carrying phase in QFM samples is a Mg- and Al-bearing Fe-Ti-Cr oxide, with increasing Cr substitution over Ti during early, rapid crystallization. Under more reducing conditions, the meteorite-based samples show evidence for increased impurity substitution, while the terrestrial-type samples appear to have a phase closer to pure magnetite. Magnetic grain size is controlled by fO2, cooling rate, and sample composition; the smallest grains form under reducing conditions, while the largest grains form under QFM conditions and at slow cooling rates. Magnetic intensity is most strongly influenced by fO2, with more subtle composition and cooling-rate effects. Moderately oxidizing QFM conditions reliably result in an intense magnetization, especially in the meteorite-derived basalts. However, an increase of grain size into the multi- domain range (meteorite-type) and/or low unblocking temperatures resulting from increased Cr- and Al- substitution (terrestrial-type) may affect the long-term stability of the remanence in QFM samples. A (significantly weaker) remanence acquired under reducing conditions is more likely to persist in samples of terrestrial composition, which are characterized by higher unblocking temperatures.